Anionic polymerization techniques have been used to synthesize polymers that are useful in the manufacture of polymers, including rubbers. Certain initiators impart a functional group to the polymers, and these functional groups are believed to have a beneficial impact on the performance of polymers.
One type of anionic polymerization is anionic living polymerization. This form of polymerization is called “living” or “controlled polymerization” as the ability of a growing polymer chain to terminate has been removed. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar (i.e. they have a very low polydispersity index). Living polymerization is one method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer. Additional advantages are predetermined molar mass and control over end-groups.
Anionic polymerization using alkali metals, radical anions, alkyllithium compounds, and lithium amides as initiators for anionic polymerization of dienes and aromatic vinyls is known. Examples of such initiator systems are disclosed in the following references: H. L. Hsieh, R. P. Quirk, “Anionic Polymerization, principles and practical applications” Marcel Dekker, Inc., New York, 1996; R. P. Quirk, S. H. Jang, “Recent advances in anionic synthesis of functionalized elastomers using functionalized alkylithium initiators”, Rubb. Chem. Thechnol., 1996, 69(3), 444-461; Y. S. Yu, R. Jérôme, R. Faft, Ph. Teyssié, “Efficiency of the sec-Butyllithium/m-Diisopropenylbenzene Diadduct as an Anionic Polymerization initiator in Apolar Solvents”, Macromolecules, 1994, 27, 5957-5963; F. Bandermann, H. D. Speikamp, L. Weigel, “Bifunctional anionic initiators: A critical study and overview”, Makromol. Chem. 1985, 186, 2017-2024; and Rachid Matmour, Arvind S. More, Prakash P. Wadgaonkar, and Yves Gnanou, “High performance poly(styrene-b-diene-b-styrene) triblock copolymers from a hydrocarbon-soluble and additive-free dicarbanionic initiator”, J. Am. Chem. Soc. 2006, 128(25), 8158-8159. U.S. Pat. No. 5,329,005, issued Jul. 12, 1994, and entitled “Soluble Anionic Polymerization Initiators and Preparation Thereof,” discloses mono lithio amine initiators.
Organo dilithio compounds are of special interest as bifunctional initiators in the anionic polymerization of dienes. The sec-butylithium/1,3-diisopropenylbenzene/triethylamine adduct, for example, is saved as difunctional lithium initiator (DiLi). However, this DiLi system requires polar additive triethylamine (Et3N) as solvent to prevent the aggregation of 1,3-diisopropenylbenzene, and combine with sec-butyl lithium, the major drawbacks of which are that it requires pre-reaction steps to synthesize the initiator, low initiator concentration, bi-modal initiation, and difficulty to make the low vinyl polybutadiene polymers.
Therefore, although alkali metal, mono-functional initiators such as alkyl lithium and lithium amides are known, and DiLi systems are known, multifunctional lithiated amine-containing initiators are not well known.